1. Field of the Invention
The present invention relates to a guide vane ring of a turbomachine, in particular of an axial-throughflow turbine or a compressor, in particular of a gas turbine. The invention relates, moreover, to a method of a modification of a guide vane ring of this type.
2. Brief Description of the Related Art
A guide vane ring conventionally consists of a plurality of vanes which are arranged next to one another in the circumferential direction and in this case are fastened to an annular vane carrier individually or in groups comprising a plurality of vanes. This vane carrier, which conventionally consists of two semiannular or semicircular parts, is itself fastened to a casing of the turbomachine. Conventionally, the vane carrier for the guide vane ring possesses an inflow-side inlet groove and an outflow-side outlet groove. These grooves in this case extend in the circumferential direction. The vanes or vane groups have in each case a vane root which has an inflow-side inlet flange and an outflow-side outlet flange. The flanges, too, extend in the circumferential direction and in this case project axially from the respective vane root. In the mounted state, the inlet flanges engage into the inlet groove and the outlet flanges into the outlet groove. The terms “inflow-side” and “outflow-side” relate to the flow direction in the region of the guide vane ring which prevails when the turbomachine is in operation.
Where large vanes and, in particular, large vane groups are concerned, it is customary for the flanges to be supported on the vane carrier in the region of the respective groove both radially on the inside and radially on the outside. A particularly intensive fastening of the vanes on the vane carrier can thereby be achieved, this also being required in order to support the high flow forces or pressure differences which may occur when the turbomachine is in operation. Precisely where large vanes are concerned, the vane carriers are also very large components which are exposed to different thermal loads when the turbomachine is in operation. On the one hand, when the turbomachine is in operation, particularly in the case of a turbine, there are pronounced temperature differences between a cooling gas and a hot gas. On the other hand, pronounced temperature differences arise even in hot gas when the latter expands during its passage through the respective turbine stage. The thermal loads vary during transient operating states, that is to say, for example, when the turbomachine is being run up and when it is being shut down. Varying thermal loads on the vane carrier may deform this. In this case, a kind of ovalization is regularly to be observed, in which the two vane carrier halves which butt against one another at their circumferential ends in a parting plane widen along the parting plane, so that the radii of the vane carrier parts increase at circumferential ends bearing against one another or contract in the region of the parting plane, with the result that the radii of the vane carrier parts having circumferential ends bearing against one another are reduced. At the same time, this may give rise to distortion within the vane carrier.
Moreover, greater deformations regularly occur at the lower vane carrier part than at the upper vane carrier part which is conventionally incorporated considerably more efficiently into the casing of the turbomachine. Said deformations of the vane carrier are transferred via the grooves to the flanges and therefore via the vane roots into the vanes or into the vane groups, with the result that these, too, are exposed to high stresses. Furthermore, the vanes may be supported against one another in the circumferential direction, radially on the inside, via shrouds, thus generating additional stresses in these when the vanes change their position as result of deformation of the vane carrier.
Said distortions may cause cracks and reduce the useful life of the vanes. In the worst case, a failure of the turbomachine may occur.